Simplify to lowest terms. $\dfrac{21}{28}$
What is the greatest common factor (GCD) of 21 and 28? $21 = 3\cdot7$ $28 = 2\cdot2\cdot7$ $\mbox{GCD}(21, 28) = 7$ $\dfrac{21}{28} = \dfrac{3 \cdot 7}{ 4\cdot 7}$ $\hphantom{\dfrac{21}{28}} = \dfrac{3}{4} \cdot \dfrac{7}{7}$ $\hphantom{\dfrac{21}{28}} = \dfrac{3}{4} \cdot 1$ $\hphantom{\dfrac{21}{28}} = \dfrac{3}{4}$